This proposal investigates the hypothesis that the disintegration of the activin signaling pathway greatly contributes to pituitary tumorigenesis. Activin and its receptors are part of the superfamily of TGF beta molecules. Activin has been shown to decrease secretion of growth hormone in the GH3 rat somatotroph and adrenocorticotropin in Att20 mouse corticotroph cell lines. It has also been shown to decrease proliferation of pituitary adenoma cells in vitro. The drosophila protein Decapentaplegic (DPP) is a homologue of human Bone Morphogenic Protein (BMP), another member of the TGF beta superfamily. Mothers Against DPP (MAD) acts downstream of DPP. Recent advances show that human homologues of MAD are involved in activin signaling and may act as tumor suppressor proteins. The long term objectives of this proposal are to advance our understanding of the role of MAD proteins in pituitary tumorigenesis and in activin signaling in the pituitary. The yeast 2 hybrid system will determine whether-MAD proteins bind activin receptors. Wildtype and truncated MAD proteins will be expressed in GH3 and Att2O cell lines to functionally define MAD homology involved in activin signaling in the pituitary This will permit the study of MAD protein phosphorylation by activin in these cell types and help elucidate the effects of MAD isoforms on proliferation. RT-PCR will determine whether mad genes are transcribed in normal and adenomatous human pituitary tissue. RNase protection will demonstrate whether mutations in MAD proteins are present in human pituitary tumors.